This invention relates to cathode for use in the electrolytic recovery of copper and, more particularly, relates to cathode starter sheets formed of stainless steel for electrorefining or electrowinning of copper.
The use of the cathodic stainless steel starter sheets as a replacement for thin sheets of high purity copper in the electrolytic recovery of copper is described in Canadian Pat. No. 910844 issued Sept. 26, 1972. The starter sheets are secured to hanger bars by means of mechanical fasteners such as bolts or rivets which pass through lugs formed at the top of the sheets. Mechanical fasteners however are prone to corrosion and may provide poor electrical conductivity between cathode components.
Canadian Pat. No. 936835 issued Nov. 13, 1973, which relates to a cathode similar in structure to the cathode shown in Canadian Pat. No. 910844, discloses shrink-fitted corrosion-resistant insulating material enveloping the vertical side edge of the cathode plate.
A stainless steel starter sheet is also disclosed in Canadian Pat. No. 1150669 issued July 26, 1983. This patent discloses a stainless steel starter sheet welded by its upper edge to the underside of a stainless steel hanger bar.
Conventional electrorefining and electrowinning plants which use copper starter sheets have an existing supply of iron hanger bars. In that stainless steel starter sheets are not easily welded to iron, mild steel or copper-clad bars, however, it normally is not practicable to use existing bars in a conversion to a stainless steel starter sheet system.
Welding of stainless steel to copper clad iron hanger bars by conventional use of monel, inconel or copper (1% tin) as filler material has not proven successful. Both monel and copper (1% tin) welds exhibit excessive corrosion in the electrolyte and inconel welds cause deformation of the hanger bar and perforation of copper cladding to expose the core metal.
It is an object of the present invention, therefore, to provide a novel re-usable cathode starter sheet of stainless steel joined to a copper clad iron hanger bar thereby permitting retrofit and use of existing iron hanger bars with substantial savings.
It is another object of the present invention to provide a method of welding stainless steel starter sheets to copper clad iron hanger bars whereby the hanger bars are not deformed by twisting or bending during the welding operation so that the starter sheets will be suspended vertically from the hanger bars.
A further object of the present invention is the provision of a cathode structure which provides good mechanical connection between the stainless steel starter sheets and copper clad hanger bars to enhance weldability of the starter sheets to the hanger bars and to provide optimum electrical contact therebetween.